1. Field of the Invention
This invention relates to a method and apparatus for operating a heater, such as a gaseous fuel fired water heater. This invention also relates to a water heater having two or more burner assemblies and a mounting apparatus for releasably attaching each burner assembly to a bottom wall of a combustion chamber, such as a water heater combustion chamber.
2. Description of Related Art
Many conventional water heater combustion chambers intentionally operate with a combustion chamber that is substantially sealed, except for communication with the surrounding environment through a flue stack and an inlet opening for fuel and/or air. In some designs, the combustion air is introduced into the combustion chamber through a restricted opening, wherein a portion of the air is mixed with fuel in the burner nozzle and ignited in a primary combustion region and the remaining portion of the air is directed around the burner to complete combustion. The remainder of the combustion chamber is substantially sealed. U.S. Pat. No. 5,797,355 describes such a gas-fired heater. The purpose of the restricted air opening in the combustion chamber is to prevent a combustion flame from passing from the combustion chamber to the ambient surroundings.
Alternatively, the heater may be constructed with a substantially sealed combustion chamber in which all or substantially all of the combustion air and fuel are directed through an inlet nozzle to the burner, denoted as a fully premixed or simply premixed burner, with the intent of improving burner and overall system performance. For example, U.S. Pat. No. 5,355,841 describes a gas-fired heater with a premixed burner having a substantially sealed combustion chamber. It is apparent that many conventional designs having premixed burner systems try to achieve a gas tight seal between the combustion chamber and a tank wall in order to limit the entry of secondary combustion air.
A common phenomenon associated with water heater designs employing premixed burners is an undesirable noise, upon ignition and during steady state operation of the combustion chamber. The noise is initiated by the transient pressure rise associated with burner ignition, and may persist during steady state operation if one or more frequencies generated by flame instabilities or other periodic energy input from the burners corresponds with one or more structural or fluidic natural frequencies of the water heater and if there is insufficient system damping to mitigate the acoustic response. Various approaches have been taken to provide noise reduction and/or pressure relief in the substantially sealed combustion chamber, as taught in U.S. Pat. Nos. 5,317,992, 5,435,716 and 5,791,298, including insulation provided on the interior of the combustion chamber, a diaphragm on the bottom of the combustion chamber, and openings in the combustion chamber covered by porous material or flaps. These approaches add to system cost and manufacturing complexity, and introduce additional components that can negatively impact reliability.